1. Field of the Invention
This invention relates to a method for production of shaped bodies of metal salts of polyacrylic acid.
The shaped bodies of metal salts of polyacrylic acid has high heat-resistant property and high modulus of compression-elasticity, hence they are useful in various industrial fields such as gears in machinery, materials in aeronautics, materials in architectural construction, and materials in electrical and electronics apparatuses and appliances.
2. Description of Prior Arts
As the method for shaping sodium polyacrylate, there has already been known one, in which the chemical compound is dissolved in an aqueous solvent and then the solution is cast into film form (see "Proceeding of Royal Society" by L. E. Nielson et al., 1964, 282A, page 137).
There has also been known a method, in which a mixture of polyacrylic acid powder and a divalent metal oxide is charged into a metal mold, then this metal mold is heated to a temperature higher than the melting point of polyacrylic acid to melt and react with the metal oxide to produce a metal salt of polyacrylic acid, and the metal salt is shaped under pressure into a desired configuration (see "Ion-Containing Polymers" by R. S. Stei, 1977).
The film as obtained by the above-mentioned casting method is very brittle, and contains many cracks and breakages, which is therefore of no practical use.
According to the above-mentioned latter method of reacting the molten polyacrylic acid and divalent metal oxide within the metal mold, the uniform mixing of both polyacrylic acid and metal oxide cannot be done, and moreover the reaction between polyacrylic acid and metal oxide cannot be effected stoichiometrically with the consequence that unreacted metal oxide remains in the shaped body in the form of a filler, which causes cavities and non-uniform portions within the resulting shaped body, thus cracks and breakages readily occur in the shaped body. Furthermore, according to the latter method, the mold-releasing property of the shaped body in inferior.
Moreover, according to the conventional techniques of forming the shaped body, the metal species for the metal salt of polyacrylic acid to be molded into the shaped body was limited to a small number such as alkali metal, alkaline earth metal, zinc, and others, because of limitation in solubility of the metal salt of polyacrylic acid, and reactivity between polyacrylic acid and metal oxide.